Hello,

I've just started using torchio and used quickstart as example to the project I want to start. I've encountered a error:

``` NameError Traceback (most recent call last) <ipython-input-5-df67c26faa17> in <module> 20 # apply RandomAffine 80% of the times and RandomElasticDeformation the rest 21 # Also, there is a 25% chance that none of them will be applied ---> 22 spatial = OneOf({ 23 tio.RandomAffine(): 0.8, 24 tio.RandomElasticDeformation(): 0.2,

NameError: name 'OneOf' is not defined ```

As you can see, quickstart guide gives error saying that `OneOf`

is not defined, and it's not imported anywhere, so I was like "Hmm... Is it torch, albumentation or torchio implementation?". Then I looked at transofrmation and found that there is an implementation of `OneOf`

, so I simply added `tio.`

to `OneOf`

and it worked.

With this PR I just want it to be fixed for everyone so that they will not have to spend extra time looking for their answer (which `OneOf`

is that). Also it'll be helpful for starters to have working solution :)